the number of grays increases, thereby producing a longer scale of contrast

as screen speed increases, so does

contrast (resulting in a shorter scale of contrast).

An increase in mAs is frequently accompanied by an appropriate decrease in

kilovoltage, which would also shorten the contrast scale.

SID and radiographic contrast are

unrelated

Grid ratio is defined as

the height of the lead strips compared to (divided by) the width of the interspace material

The width of the lead strips has no bearing on the

grid ratio.

Although the stated focal spot size is measured directly under the actual focal spot, focal spot size really varies along the length of the x-ray beam. At which portion of the x-ray beam is the effective focal spot the largest?

At the cathode end

X-ray tube targets are constructed according to the

line focus principle—the focal spot is angled (usually 12° to 17°) to the vertical

As the actual focal spot is projected downward, it is foreshortened; thus, the effective focal spot is always smaller than the

actual focal spot

As it is projected toward the cathode end of the x-ray beam, the effective focal spot becomes larger and approaches the

actual size

As it is projected toward the anode end, it gets smaller because of the

anode "heel" effect.

How are mAs and radiographic density related in the process of image formation?

mAs and radiographic density are directly proportional.

Radiographic density is described as the

overall degree of blackening of a radiograph or a part of it.

The mAs regulates

the number of x-ray photons produced at the target, and thus regulates radiographic density

mAs and radiographic density are directly

proportional

The speed of an intensifying screen is influenced by which of the following factors?

1. Phosphor layer thickness2.. Phosphor type used

Rare earth phosphors have a much higher conversion efficiency (and therefore speed) and have all but replaced the older

calcium tungstate screens.

The larger the phosphor and the thicker the layer of phosphors (active layer), the greater the light emission and therefore the

speed.

Antihalation backing

a component of single-emulsion film that prevents crossover of fluorescent light within an image receptor.

In radiography of a large abdomen, which of the following is (are) effective way(s) to minimize the amount of scattered radiation reaching the IR?

1. Use of close collimation2. Use of compression devices

One way to minimize scattered radiation reaching the IR is to use

optimal kilovoltage

excessive kVp increases the production of

scattered radiation.

Close collimation is also important because

the smaller the volume of irradiated material, the less scattered radiation is produced

Using compression bands or the prone position in a large abdomen has the effect of making the abdomen "thinner"; it will therefore generate less

scattered radiation

Low-ratio grids allow a greater percentage of

scattered radiation to reach the IR.

Use of a high-ratio grid will clean up a greater amount of

scattered radiation before it reaches the IR.

The general rule is that structures measuring more than 10 cm should be radiographed with a

grid

To produce a just perceptible increase in radiographic density, the radiographer must increase the

mAs by 30%

f a radiograph lacks sufficient blackening, an increase in

mAs is required.

mAs regulates

the number of x-ray photons produced at the target.

An increase or decrease in mAs of at least

30% is necessary to produce a perceptible effect.

Increasing the kVp by 15% will have about the same effect as

doubling the mAs.

The mAs is the exposure factor governing radiographic

density.

Which of the following influences geometric unsharpness?

1. OID2. Source-object distance3. SID

As OID increases, so does

magnification

OID is directly related to

magnification

As focal-object distance and SID decrease, magnification

increases

Focal-object distance and SID are inversely related to

magnification

Greater latitude is available to the radiographer in which of the following circumstances?

1. Using high-kVp technical factors2. Using a slow film-screen combination3. Using a low-ratio grid

In the low kilovoltage ranges, a difference of just a few kVp makes a very

noticeable radiographic difference

High-kVp technical factors offer much greater margin for

error

slow film-screen combinations offer much greater margin for

error

Lower-ratio grids offer more tube-centering latitude than

high-ratio grids

Decreasing field size from 14 x 17 into 8 x 10 inches will?

decrease radiographic density and decrease the amount of scattered radiation generated within the part.

Limiting the size of the radiographic field serves to limit the amount of ?

scattered radiation produced within the anatomic part.

As the amount of scattered radiation generated within the part decreases, so does the?

resultant density within the radiographic image

beam restriction is a very effective means of reducing the quantity of non-information-carrying?

x-ray exposure to provide adequate radiographic density and cannot be used when exposure reduction or fast exposure time is essential.

because they are associated with less diffusion of fluorescent light, they produce better?

recorded detail and are used to image structures requiring excellent recorded detail.

Pediatric radiography is likely to require?

fast screens to reduce exposure time and dose.

Shape distortion is influenced by the relationship between the

1. x-ray tube and the part to be imaged.2. part to be imaged and the image recorder.3. image recorder and the x-ray tube.

Shape distortion is caused by ?

misalignment of the x-ray tube, the part to be radiographed, and the image recorder/film.

Only one of the three need be misaligned for

distortion to occur.

Which of the following devices is used to overcome severe variation in patient anatomy or tissue density, providing more uniform radiographic density?

Compensating filter

A compensating filter is used when ?

the part to be radiographed is of uneven thickness or density (in the chest, mediastinum vs lungs)

The filter (made of aluminum or lead acrylic)

is constructed in such a way that it will absorb much of the primary radiation that would expose the low-tissue density area, while allowing the primary radiation to pass unaffected to the high-tissue density area.

A collimator is used to

decrease the production of scattered radiation by limiting the volume of tissue irradiated.

t may be enhanced with high-contrast technical factors, especially using

low kilovoltage levels.

At low kilovoltage levels

the photoelectric effect predominates.

Diagnostic x-ray photons interact with tissue in a number of ways, but mostly they are involved in the production of

Compton scatter or in the photoelectric effect

Compton scatter occurs

when a relatively high-energy (kV) photon uses some of its energy to eject an outer-shell electron. In doing so, the photon is deviated in direction and becomes a scattered photon.

Compton scatter causes

objectionable scattered radiation fog in large structures such as the abdomen and poses a radiation hazard to personnel during procedures such as fluoroscopy.

In the photoelectric effect

a relatively low-energy x-ray photon uses all its energy to eject an inner-shell electron, leaving a "hole" in the K shell. An L-shell electron then drops down to fill the K vacancy, and in so doing emits a characteristic ray whose energy is equal to the difference between the binding energies of the K and L shells.

The photoelectric effect occurs with

high-atomic-number absorbers such as bone and positive contrast media, and is responsible for the production of radiographic contrast

photoelectric effect

is helpful for the production of the radiographic image, but it contributes to the dose received by the patient (because it involves complete absorption of the incident photon).

Factor(s) that can be used to regulate radiographic density is (are)

1. milliamperage.2. exposure time.3. kilovoltage.

Factors that regulate the number of x-ray photons produced at the target can be used to control

radiographic density, namely milliamperage and exposure time (mAs)

Radiographic density is directly proportional to

mAs

if the mAs is cut in half, the radiographic density will decrease by

one-half

Although kilovoltage is used primarily to regulate radiographic contrast, it may also be used to regulate

radiographic density in variable-kVp techniques, according to the 15% rule.

An increase in the kilovoltage applied to the x-ray tube increases the

exposure rate.

As the kilovoltage is increased,

a greater number of electrons are driven across to the anode with greater force.

as energy conversion takes place at the anode,

more high-energy (short-wavelength) photons are produced.

because they are higher energy photons, there will be less

patient absorption.

OID is related to recorded detail in which of the following ways?

Radiographic detail is inversely related to OID.

As the distance from the object to the IR (OID) increases, so does

magnification distortion thereby decreasing recorded detail.

Which of the following examinations might require the use of 120 kVp?

1. Chest radiograph2. Barium-filled stomach

High-kilovoltage factors are frequently used to even out densities in anatomic parts with high

tissue contrast (eg, the chest)

as high kilovoltage produces added scattered radiation, it generally must be used with a

grid

It would be inappropriate to perform an AP abdomen with high kilovoltage because it has such low

subject contrast

Barium-filled structures are frequently radiographed using 120 kV or more to penetrate the barium—to see

through to structures behind.

Radiographic contrast is the result of

differential absorption

Differential absorption refers to

the x-ray absorption characteristics of neighboring anatomic structures—determined by the atomic number of the tissue being examined.

The radiographic representation of these various density structures is referred to as

radiographic contrast; it may be enhanced with high-contrast technical factors, especially using low kilovoltage levels.

At low kilovoltage levels,

the photoelectric effect predominates.

If photons are absorbed, there will be no

contrast

The technical factor milliampere-seconds is used to regulate

image density.

when two or more characteristic curves are being compared, the fastest film emulsion is the one furthest to the

left

sensitivity =

speed

Screen-film imaging is one example of a (n)

analog system

Screen-film imaging consists of an exposure method of converting x-ray energy to

light energy, then converting light energy to electrochemical energy in the development process.

Processing changes the invisible electrochemical image to a

visible/manifest radiographic image

This process ends with

analog data

Digital imaging is

an electronic imaging method that allows data capture and manipulation in an electron pattern.

The resulting image can be turned into an analog image after going through

several energy changes (electron to light to film or TV screen).

The direct action of x-rays has very little influence on

a radiographic image produced with intensifying screens (fluorescent light is responsible for the majority of film exposure).

If the imaging system speed is cut in half (from 400 to 200 speed), the result will be

half of the original density on the radiograph

Because the grid removes scattered (and some primary) radiation from the beam, an

increase in exposure factors is required.

Which of the following combinations will result in the most scattered radiation reaching the image receptor?

Using fewer mAs and more kVp

As x-ray photons travel through a part, they either pass all the way through to expose the film/image receptor, or they

undergo interaction(s) that may result in their being absorbed by the part or deviated in direction.

It is those that change direction (scattered radiation) that

undermine the image

Scattered radiation adds

unwanted, degrading densities to the radiographic image.

The single most important way to reduce the production of scattered radiation is to

collimate

Although collimation, use of lower kVp (with appropriately higher mAs), and compression can be used, a large amount of scattered radiation is still generated within the part being radiographed and, because it adds unwanted noninformation-carrying densities, it can have a severely degrading effect on image quality, thus the need for

grids

X-ray photon energy is inversely related to

photon wavelength

As kVp is increased,

more high-energy photons are produced and the overall energy of the primary beam is increased.

Minimizing magnification through the use of increased SID and decreased OID functions to improve

recorded detail.

For which of the following examinations can the anode heel effect be an important consideration?

1. Lateral thoracic spine2. AP femur

The heel effect is characterized by a variation in beam intensity, which gradually increases from

anode to cathode

the AP thoracic spine is thicker

caudally than cranially, and so the thicker portion is best placed under the cathode

in the lateral projection of the thoracic spine, the upper portion is

thicker because of superimposed shoulders, and therefore that portion is best placed under the cathode end of the beam.

The femur is also uneven in density, particularly in the

AP position, and can benefit from use of the heel effect

The anode heel effect is most pronounced when using

large-size IRs, at short SIDs, and with an anode having a steep (small) target angle.

If the radiographer is unable to achieve a short OID because of the structure of the body part or patient condition, which of the following adjustments can be made to minimize magnification distortion?

A longer SID should be used.

An increase in SID will help decrease the effect of excessive

OID

especially with larger body parts, increased SID usually requires a significant increase in

exposure factors.

Focal spot size, screen speed, and grid ratio are unrelated to

magnification.

Which of the following would be useful for an examination of a patient suffering from Parkinson's disease?

1. High-speed screens2. Short exposure time

Which of the following may be used to reduce the effect of scattered radiation on the finished radiograph?

1. Grids2. Collimators3. Compression bands

Collimators

restrict the size of the irradiated field, thereby limiting the volume of irradiated tissue, and hence less scattered radiation is produced.

Once radiation has scattered and emerged from the body, it can be trapped by

the grid's lead strips

Grids effectively remove much of the scattered radiation in the remnant beam before it reaches the

x-ray IR

Compression can be applied to

reduce the effect of excessive fatty tissue (eg, in the abdomen), in effect reducing the thickness of the part to be radiographed.

Compared to a low ratio grid, a high ratio grid will

1. absorb more primary radiation.2. absorb more scattered radiation.

The higher the lead strips (or the smaller the distance between the strips), the greater the

grid ratio and the greater the percentage of scattered radiation absorbed

a grid does absorb some

primary radiation as well.

The higher the lead strips, the more critical the need for

accurate centering, as the lead strips will more readily trap photons whose direction do not parallel them

The reduction in x-ray photon intensity as the photon passes through material is termed

attenuation

Absorption

occurs when an x-ray photon interacts with matter and disappears, as in the photoelectric effect

Scattering

occurs when there is partial transfer of energy to matter, as in the Compton effect.

attenuation

The reduction in the intensity of an x-ray beam as it passes through matter

for a short time after the exposure has terminated. This characteristic (phosphorescence) is a desirable quality in fluoroscopic screens.

Lag

occurs when an intensifying (radiographic) screen continues to fluoresce after the x-ray stimulation has terminated. This characteristic is undesirable and causes excessive density.

Screen speed is identified by

the amount of light emitted by the phosphors.

Which of the following technical changes would best serve to remedy the effect of widely different tissue densities?

High kVp exposure factors

When tissue densities within a part vary greatly (eg, chest x-ray), the radiographic result can be

unacceptably high contrast.

To "even out" these densities and produce a more appropriate scale of grays, exposure factors using

high kVp should be employed

Radiographic contrast generally increases with

an increase in screen speed.

The higher the grid ratio, the higher the

contrast.

Exposure factors using high mAs generally result in

excessive image density, frequently obliterating much of the gray scale.

Congestive heart failure, pneumonia, and pleural effusion, all involve abnormal amounts of fluid in the chest and would therefore require

an increase in exposure factors.

An increase in kilovoltage will serve to

produce a longer scale of contrast

An increase in kilovoltage increases

the overall average energy of the x-ray photons produced at the target, thus giving them greater penetrability. (This can increase the incidence of Compton interaction and therefore the production of scattered radiation.)

Greater penetration of all tissues serves to

lengthen the scale of contrast.

excessive scattered radiation reaching the IR will cause

a fog and carries no useful information.

Focusing distance is associated with which of the following?

Grids

Focusing distance

the term used to specify the optimal SID used with a particular focused grid.

Focusing distance is usually expressed as

focal range, indicating the minimum and maximum SID workable with that grid.

Lesser or greater distances can result in

grid cutoff

Which of the following absorbers has the highest attenuation coefficient?

Bone

The atomic number (Z) of the tissues under investigation is directly related to

its attenuation coefficient

differential absorption

contributes to the various shades of gray (scale of radiographic contrast) on the finished x-ray image.

effective Z number

Air has an effective Z number of 7.78, fat is about 6.46, water is 7.51, muscle is 7.64, and bone is 12.31.

As the object-to-image receptor distance (OID) increases, magnification of that object

increases.

The formula used to determine image width is:

iw = SID`````` ````````` ow SOD

Osteoporosis

a condition, often seen in the elderly, marked by increased porosity and softening of bone. The bones are much less dense, and thus a decrease in exposure is required.

Osteomyelitis and osteochondritis

inflammatory conditions that usually have no effect on bone density.

Osteosclerosis

abnormal hardening of the bone, and an increase in exposure factors would be required.

Exposure rate increases with an increase in

1. mA.2. kVp.

quantity of x-ray photons produced at the target is the function of

mAs

quality (wavelength, penetration, energy) of x-ray photons produced at the target is the function of

kVp

kVp also has an effect on exposure rate, because

an increase in kVp will increase the number of high-energy x-ray photons produced at the target.

The intensity of scattered radiation 1 m from the patient is approximately

0.1% of the intensity of the primary beam

Distortion can be caused by

1. tube angle.2. the position of the organ or structure within the body.3. the radiographic positioning of the part.

Increasing the grid ratio will result in a larger percentage of scattered radiation being absorbed and hence a

shorter scale of contrast.

The function(s) of automatic beam limitation devices include

reducing the production of scattered radiation.

Beam restrictors

function to limit the size of the irradiated field. In doing so, they limit the volume of tissue irradiated (thereby decreasing the percentage of scattered radiation generated in the part) and help reduce patient dose.

Beam restrictors do not affect

the quality (energy) of the x-ray beam—that is the function of kVp and filtration

Beam restrictors do not absorb scattered radiation—that is a function of

grids

The formula used to determine the amount of image magnification is:

image size = SID`````````````` `````object size SOD

mAs has no effect on

the scale of contrast produced

slower screens will produce

lower (longer scale) contrast than faster screens

lower grid ratios produce

longer scale than higher grid ratios

As the volume of irradiated tissue increases, so does the amount of

scattered radiation produced and, consequently, the longer the scale of radiographic contrast

As kVp is reduced, the number of high-energy photons produced at the target is reduced; therefore, a decrease in

radiographic density occurs.

If a radiograph exhibits insufficient density, this might be attributed to

Which of the following quantities of filtration is most likely to be used in mammography?

0.5 mm Mo

Soft tissue radiography requires the use of

long-wavelength, low-energy x-ray photons.

Very little filtration is used in

mammography.

anything more than 1.0 mm of aluminum would

remove the useful soft photons, and the desired high contrast could not be achieved.

Dedicated mammographic units

usually have molybdenum targets (for the production of soft radiation) and a small amount of molybdenum filtration.

Which of the following are methods of limiting the production of scattered radiation?

1. Using the prone position for abdominal examinations2. Restricting the field size to the smallest practical size

Beam restriction is probably the single most effective means of

reducing the production of scattered radiation.

Grid ratio affects

the cleanup of scattered radiation; it has no effect on the production of scattered radiation

Radiographic contrast is a result of

1. differential tissue absorption.2. emulsion characteristics.

Radiographic contrast

the degree of difference between adjacent densities.

These density differences represent

sometimes very subtle differences in the absorbing properties of adjacent body tissues.

type of film emulsion used also brings with it its own

contrast characteristics

Different types of film emulsions have different degrees of

contrast "built into" them chemically.

The technical factor used to regulate contrast is

kilovoltage.

With a given exposure, as intensifying-screen speed decreases, how is radiographic density affected?

Decreases

As intensifying-screen speed decreases,

less fluorescent light is emitted from the phosphors.

If less fluorescent light strikes the film emulsion,

a smaller number of silver halide grains are changed to black metallic silver in the developer, and hence there is a decrease in radiographic density.

As intensifying-screen speed decreases, so does

radiographic density

Intensifying-screen speed and radiographic density are

directly related.

Because the anode's focal track is beveled

(angled, facing the cathode), x-ray photons can freely diverge toward the cathode end of the x-ray tube.

the "heel" of the focal track prevents x-ray photons from

diverging toward the anode end of the tube. This results in varying intensity from anode to cathode, with fewer photons at the anode end and more photons at the cathode end.

The anode heel effect is most noticeable when using

large IR sizes, short SIDs, and steep target angles.

The formula used to determine magnification factor is:

MF = SID/SOD

if MF = 1.257

The "1" represents the actual object, while the ".257" represents the degree of magnification. The percent magnification can be determined by moving the decimal two places to the right. Thus, the percent magnification is 25.7%.

Which of the following contribute to the radiographic contrast present on the finished radiograph?

1. Atomic number of tissues radiographed2. Any pathologic processes3. Degree of muscle development

The atomic number of the tissues under investigation is directly related to their

attenuation coefficient.

differential absorption contributes to

the various shades of gray (scale of radiographic contrast) on the finished radiograph.

Normal tissue density may be significantly altered in the presence of

pathologic processes.

What determines the quantity of fluorescent light emitted from a fluorescent screen?

1. Thickness of the phosphor layer2. Type of phosphor used3. kV range used for exposure

The thicker the layer of phosphors,

the more fluorescent light is emitted from the screen

Different types of phosphors have different

conversion efficiencies; rare earth phosphors emit more light during a given exposure than do calcium tungstate phosphors.

As the kVp level is increased,

so is the amount of fluoroscopic light emitted by intensifying-screen phosphors.

Why are a single intensifying screen and single emulsion film used for select radiographic examinations?

For better recorded detail

The diffusion of fluorescent light from intensifying screens is responsible for

a loss of recorded detail on double-emulsion film.

by changing the system to include only one intensifying screen and single-emulsion film, as in mammographic systems, light diffusion is reduced and better

recorded detail results.

Patient dose is somewhat greater than with a two-screen cassette system, but the advantage of significantly improved

recorded detail greatly offsets this.

The major function of filtration is to reduce

patient dose

X-rays produced at the target make up a

heterogeneous primary beam

There are many "soft," low-energy photons that, if not removed, would contribute only to

greater patient (skin) dose

They do not have enough energy to penetrate the patient and expose the film; they just

penetrate a small thickness of the patient's tissue and are absorbed.

These photons are removed by

aluminum filters

A shoulder was imaged using 300 mA, 7 ms, 70 kVp, 40-inch SID, 1.2-mm focal spot, and 100 speed screen/film combination. Which of the following changes, made to compensate for changes in optical density, would result in decreased production/visualization of blur?

1. Use of a 0.6-mm focal spot2. Use of a 50-inch SID

Blur impairs

recorded detail

The factors that affect the recorded detail of traditional screen/film imaging are

Use of a higher-speed film-screen combination also helps reduce mAs (exposure time) through

more efficient conversion of photon energy to fluorescent light energy.

Methods that help reduce the production of scattered radiation include using

1. compression.2. beam restriction.

Limiting the size of the irradiated field is a most effective method of

decreasing the production of scattered radiation

The smaller the volume of tissue irradiated, the smaller the amount of

scattered radiation generated; this can be accomplished using compression (prone position instead of supine or a compression band)

The single most important factor regulating radiographic contrast is

kVp

The lower the kVp

the shorter the scale of contrast.

Grid ratio

defined as the ratio between the height of the lead strips and the width of the distance between them (ie, their height divided by the distance between them).

The thickness of the lead strip is unrelated to

grid ratio.

Why is a very short exposure time essential in chest radiography?

To minimize involuntary motion

All of the following affect the exposure rate of the primary beam

A. mA.B. kVp.C. distance.

Exposure rate is regulated by

milliamperage.

Distance significantly affects the exposure rate, according to the

inverse square law of radiation.

Kilovoltage also has an effect on exposure rate, because

an increase in kVp will increase the number of high-energy photons produced at the target.

The size of the x-ray field determines

the volume of tissue irradiated, and hence the amount of scattered radiation generated, but is unrelated to the exposure rate.

Which of the following is (are) causes of grid cutoff when using reciprocating grids?

1. Inadequate SID

If the SID is above or below the recommended focusing distance, the primary beam will not coincide with the angled lead strips at their lateral edges. Consequently, there will be absorption of the primary beam, termed

grid cutoff.

If the central ray is off-center longitudinally, there will be

no ill effects

If the central ray is off-center side-to-side, the lead strips are no longer parallel with the divergent x-ray beam, and there will be

loss of density due to grid cutoff.

Central ray angulation in the direction of the lead strips is appropriate and will not cause

grid cutoff

Central ray angulation against the direction of the lead strips will cause

The variation in photon distribution between the anode and cathode ends of the x-ray tube is known as

the anode heel effect

Because the focal spot (track) of an x-ray tube is along the anode's beveled edge

photons produced at the target are able to diverge toward the cathode end of the tube, but are absorbed by the "heel" of the anode at the opposite anode end of the tube

This results in

a greater number of x-ray photons distributed toward the cathode end and is known as the anode heel effect.

line focus principle

is a geometric principle illustrating that the effective focal spot is always smaller than the actual focal spot.

Bohr's theory

refers to an atom's resemblance to the solar system

reciprocity law

states that a particular mAs, regardless of the mA and exposure time used, will provide identical radiographic density.

This holds true with direct exposure techniques, but it does fail somewhat with

the use of intensifying screens. However, the fault is so slight as to be unimportant in most radiographic procedures.

most likely to be the cause of quantum mottle.

Fast imaging systems (fast film and fast screens, as well as CR/DR systems) with low mAs and high kVp factors

Recorded detail is unaffected by changes in

kVp

When changing from single-phase to three-phase, six-pulse equipment,

two-thirds of the original mAs is required to produce a radiograph with similar density

When changing from single-phase to three-phase, 12-pulse equipment,

only one-half of the original mAs is required.

Which of the following affect(s) both the quantity and the quality of the primary beam?

1. Half-value layer (HVL)2. kVp

The principal qualitative factor for the primary beam is

kVp, but an increase in kVp will also create an increase in the number of photons produced at the target.

HVL

the amount of material necessary to decrease the intensity of the beam to one half of its original value, thereby effecting a change in both beam quality and quantity.

The mAs value is adjusted to regulate

the number of x-ray photons produced at the target.

X-ray beam quality is unaffected by changes in

mAs

The use of which of the following is (are) essential in magnification radiography?

Fractional focal spot

Magnification radiography is used to

enlarge details to make them more perceptible

candidates for magnification radiography

Hairline fractures, minute blood vessels, and microcalcifications

The problem of magnification unsharpness is overcome by using a

fractional focal spot;

larger focal spot sizes will produce

excessive blurring unsharpness

Grids are usually unnecessary in magnification radiography because of

the air-gap effect produced by the OID

A direct-exposure technique would not be likely to be used because of

the excessive exposure required.

A compensating filter is used to

even out widely differing tissue densities

For example

it is difficult to obtain a satisfactory image of the mediastinum and lungs simultaneously without the use of a compensating filter to "even out" the densities. With this device, the chest is radiographed using mediastinal factors, and a trough-shaped filter (thicker laterally) is used to absorb excess photons that would overexpose the lungs. The middle portion of the filter lets the photons pass to the mediastinum almost unimpeded.

Which of the following factors influence(s) the production of scattered radiation?

1. Kilovoltage level2. Tissue density3. Size of field

Beam restriction is the single most important way to limit the amount of

scattered radiation produced

The absorption of useful radiation by a grid is called

grid cutoff.

contrast improvement factor.

Contrast obtained with a grid compared to contrast without a grid

he greater the percentage of scattered radiation absorbed compared to absorbed primary radiation, the greater the

"selectivity" of the grid

If a grid absorbs an abnormally large amount of useful radiation as a result of improper centering, tube angle, or tube distance